Specific gravity control apparatus and method of using same



Dec. 27, 1955 w. c. sAEMAN 2,728,690 SPECIFIC GRAVITY CONTROL APPARATUS ANO METHOD OF USING SAME: Filed Maron 51. 1953 T0 C0475 R FAN UnitedStates Patent O SPECIFIC GRAVITY CONTROL APPARATUS AND METHOD F USING SAME Walter C. Saeman, Brevard, N. C., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Application March 31, 1953, Serial No. 345,815

7 Claims. (Cl. 117-113) This invention relates in general to apparatus vfor controlling specic gravity, and more particularly to apparatus of this sort adapted especially for handling an aqueous dispersion coating composition and to the method by which such a composition may be handled through use of apparatus embodying the present invention.

In copending application Serial No. 310,396, filed September 19, 1952, there is disclosed an applicator pan construction arranged uniquely for applying to cellophane and the like an aqueous dispersion coating composition of the type disclosed in U. S. Patent No. 2,570,478, issued October 9, 1951. The applicator pan construction described in the above noted copending application provides for circulating the coating supply through the applicator pan so that a uniform distribution of the coating composition is maintained for application.

According to the present invention it has been found that the control and uniformity of coating weight obtained in applying an aqueous dispersion of the above noted type is dependent primarily on the specific gravity of the coating dispersion delivered for circulation through the applicator pan of the above identified copending'application, and the apparatus of the present invention provides means for maintaining the specific gravity of the delivered dispersion constant, and thereby obtaining application of a constant coating weight from the applicator pan, in a very effective manner. This apparatus and the manner in which it is used for the above stated purpose comprises provision for the addition of water to a continuously circulating supply of the aqueous dispersion as needed to maintain the specific gravity thereof constant in accordance with continuous specific gravity sensings made as the dispersion is delivered for coating, all as described in detail below in connection with the accompanying drawings, in which:

Fig. l is a schematic diagram of means for circulating an aqueous dispersion coating composition supply in accordance with the present invention; and

Fig. 2 is an enlarged detail showing a means for making specific gravity sensings according to the present invention in the system illustrated in Fig. l.

Referring now in detail to the drawings, and especially at rst to Fig. l, an applicator pan for applying an aqueous dispersion, as disclosed in the above identified copending application, is indicated by the reference numeral 10. A coating supply of the aqueous dispersion being handled is delivered to the applicator pan 10 through an outlet drain connection 12 from a constant head tank 14.

This head tank 14 comprises means for trapping a constant head of the aqueous dispersion as it is circulated through a supply line 16 from a feed tank 18. The above mentioned outlet connection 12 is arranged to drain to the applicator pan 10 from the constant head trapped in the head tank 14, and an overflow by which the constant head is maintained in the head tank 14 is connected through a return line 20 to drain back to the feed tank 18, as is described more in detail further below. A return line 22 is also connected from the applicator pan 10 to 2,728,690 aten'ted Dec. 27, 1955 drain back to the feed tank 18 and thereby maintain a circulating flow through the applicator pan 10, as disclosed in the above identified copending application.

The feed tank 18 is fitted with a filling line as at 24 for introducing a supply of the aqueous dispersion being handled therein from storage or the like. A suitable pump 26 is provided in the supply line 16 to effect the circulation therein of the aqueous dispersion supply from the feed tank 18 to the constant head tank 14. Also, heat exchange means 27, such as a brine cooler fitted with automatic temperature control, is included in the supply line 16 so as to maintain the aqueous dispersion circulated to the head tank 14 at a constant temperature for the specific gravity sensings. n

The manner in which the specific gravity sensings are obtained and used according to the present invention is illustrated best in Fig. 2 of the drawings, which is an enlarged detail showing the contant head tank 14 in section and the related arrangement of the specific gravity control that is indicated schematically in Fig. l at 28. The head tank 14 is shown in Fig. 2 litted with the supply line 16 from the feed tank 18, the applicator pan delivery line 12, and the constant head overflow drain line 20 that returns to the feed tank 18, as already noted above.

The specific gravity control 28 is mounted adjacent the top of the head tank 14 on a support bracket 30, and comprises a balance arm 32 having a pivot mounting at 34 and carrying an adjustable balance weight 36 on the remote side of the pivot 34 to counterbalance a displacement element 38 suspended from the adjacent end of the balance arm 32 in the constant head of aqueous dispersion maintained in the head tank 14, as previously described. As thus arranged, the specific gravity control 28 is adapted to operate by the Westphal balance principle for sensing continuously the specific gravity of the aqueous dispersion at the head tank 14 just before delivery thereof to the applicator pan 10.

In handling an aqueous dispersion as contemplated by the present invention, variations in specific gravity of the dispersion are attributable to moisture losses caused by such factors as evaporation during handling and absorption Where the coating is being done on a hydrophilic material like cellophane. The result of these losses is to make the water content of the dispersion returned to the feed tank 18 through the drain lines 20 and 22 from the head tank 14 and applicator pan 10 less than the content required to provide the specific gravity fixed upon for the dispersion supply. The returning'dispersion being poor in water acts in turn to lower the water content of the dispersion supply in the feed Vtank 18, and the ultimate result is circulation to the head tank 14 of dispersion with a specic gravity varying from the desired value, usually above the desired value. The specific gravity control 28 upon sensing this variation through the displacement element 38 will reflect it in tilting movement of the balance arm 32 (Within the limits provided by the stop bracket 40 which restrains the balance arm 32 to a suitable degree of operating movement).

In order to employ this specific gravity sensing for control purposes, a normally open electrical switch is arranged as at 42 on the support bracket 30 for operation by an adjustable actuator 44 carried on the balance arm 32. As shown in Fig. 2, the switch 42 and actuator 44 are arranged so that downward movement of the remote end of the balance arm 32, which would be caused by an increase of the dispersion specific gravity, will result in lowering the actuator 44 and thereby depressing the switch operating button indicated at 42 to close the switch 42. This switch 42 is included in an electrical circuit running as indicated at 46 to a solenoid valve 48 disposed in a water addition or make-up line 50 connected for adding water to the dispersion as it is circulated from the feed` rank is te the head tank 14. By taie arrangement, addition of Water through the line t) will besensed immediately in the head tank 14 by the specific gravity control 28, so that the balance arm 32 will return to normal and release the switch 42 to open position and thereby stop the addition of Water as soon as the specific gravity variation has been corrected. It should be noted, too, that the Water addition line 50 is shown in Fig. l connected adjacent the inlet of the circulating pump 26, which provides for thorough mixing of the added Water in the dispersion.

The present invention has been described in detail above for purposes of illustration only and is not intended to be limited by this description or otherwise exceptfas defined in the appended claims.

Y l. Apparatus for handling an aqueous dispersion coating composition, said apparatus comprising a head tank having an overtlow for maintaining a constant head therein and having a delivery outlet for draining from a constant head therein, an applicator pan from which said aqueous dispersion is applied as a coating, a feed tank for containing a supply of said aqueous dispersion, means for circulating said aqueous dispersion from said feed tank to said head tank, means for connecting said head tank overflow for draining to said feed tank, means connecting said head tank delivery outlet for draining to said applicator pan, means connecting said applicator pan 4for draining to said feed tank and thereby maintaining a circulating iiow in said applicator pan, means for adding Water to the aqueous dispersion circulated from said feed tank to said head tank, and specific gravity sensing means at said head tank for controlling said Water addition means and thereby maintaining the aqueous dispersion in said head tank at a uniform specic gravity for delivery to said applicator pan.

2. Apparatus for handling an aqueous dispersion coating composition, said apparatus comprising an applicator pan from which said aqueous dispersion is applied as a coating, a head tank from Which said aqueous dispersion is delivered to said applicator pan, a feed tank from which a supply of said aqueous dispersion is circulated to said head tank, said head tank having an overflow to said feed tank for maintaining a constant head in said head tank, said applicator pan having an overflow to said feed tank for maintaining a circulating flow in said applicator pan, means for circulating said aqueous dispersion from said feed tank to said head tank, means disposed at said head tank for sensing the specific gravity of the aqueous dispersion therein, and means controlled by said sensing means for adding Water to the aqueous dispersion circulated from said feed tank upon variation of the specific gravity thereof at said head tank from a desired level.

3. Apparatus for handling an aqueous dispersion coating composition as defined in claim 2 and further characterized in that said means for circulating the aqueous dispersion from said feed tank to said head tank comprises a pump, and said Water addition means is connected adjacent the inlet of said pump.

4. Apparatus for handling an aqueous dispersion coating composition as defined in claim 2 and further characterized in that Said aqueous dispersion is circulated from said feed tank to said head tank through heat exchange meansV formaintaining the temperature thereof constant in said head tank.

5. Apparatus for handling an aqueous dispersion coating composition as defined in claim 2 and further characterized in that said specific gravity sensing means comprises a balance arm and a displacement element suspended in said head tank from said balance arm, and said Water addition means is fitted with a solenoid valve operated by an electrical circuit including a switch actuated by said balance arm.

6. The method of handling an aqueous dispersion coating composition which comprises continuously circulating said aqueous dispersion from a feed supply thereof and trapping ar constant overow head of said circulated aqueous dispersion, continuously delivering aqueous dispersion from said trapped constant head for circulation through a coating fountain supplyV While draining the overow from said trapped constant head and the circulation through said fountain supply back to said feed supply, continuously -sensing the specific gravity of said aqueous dispersion at the trapped constant head thereof, and adding Water intermittently to the aqueous dispersion circulated from said feed supply upon variation of the sensed specific gravity at said trapped constant head from a desired value.

7. The method of handling an aqueous dispersion coating composition which comprises continuously circulating said aqueous dispersion from a feed supply thereof and trapping a constant overflow head of said circulated aqueous dispersion, continuously delivering aqueous dispersion from said trapped constant head for circulation ythrough a coating fountain supply while draining the overflow from said trapped constant head and the circulation through-said fountain supply back to said feed supply, and continuously sensing the specific gravity of said aqueous dispersion at said trapped constant head and using said sensing to effect intermittently an addition of Water to the aqueous dispersion circulated from said feed supply upon variation of the sensed specific gravity at said trapped constant head.

References Cited in the le of this patent UNITED STATES PATENTS 

6. THE METHOD OF HANDLING AN AQUEOUS DISPERSION COATING COMPOSITION WHICH COMPRISES CONTINUOUSLY CIRCULATING SAID AQUEOUS DISPERSION FROM A FEED SUPPLY THEREOF AND TRAPPING A CONSTANT OVERFLOW HEAD OF SAID CIRCULATED AQUEOUS DISPERSION, CONTINUOUSLY DELIVERING AQUEOUS DISPERSION FROM SAID TRAPPED CONSTANT HEAD FOR CIRCULATION THROUGH A COATING FOUNTAIN SUPPLY WHILE DRAINING THE OVERFLOW FROM SAID TRAPPED CONSTANT HEAD AND THE CIRCULATION THROUGH SAID FOUNTAIN SUPPLY BACK TO SAID FEED SUPPLY, CONTINUOUSLY SENSING THE SPECIFIC GRAVITY OF SAID AQUEOUS DISPERSION AT THE TRAPPED CONSTANT HEAD THEREOF, AND ADDING WATER INTERMITTENTLY TO THE AQUEOUS DISPERSION CIRCULATED FROM SAID FEED SUPPLY UPON VARIATION OF THE SENSED SPECIFIC GRAVITY AT SAID TRAPPED CONSTANT HEAD FROM A DESIRED VALUE. 